The prior art, e.g., Provost et al., Proc. Soc. Exp. Biol. Med. 142, 1257-1269 (1973) describes the detection of hepatitis A antigen in serum by means of an in vivo assay involving injecting hepatitis A containing serum into marmosets and observing the marmosets for subsequent presence of hepatitis A disease. Hepatitis A antigen has never been detected in serum by an in vitro assay.
Prior art assays for hepatitis A antibody require the use of hepatitis A antigen derived from excised liver of infected marmosets. The hepatitis A antigen is then purified. This method is very costly as the marmosets are not only expensive to purchase and maintain but are becoming increasingly scarce. The method is also time-consuming as the livers cannot be harvested until several weeks after the animal is infected.
The prior art teaches antigen assays wherein the complementary antibody is bonded to a surface and used to form an immune complex with the antigen in a test sample, Friedman et al., Immunoserology in the Diagnosis of Infectious Diseases, Sym. ASM, 1977, Univ. Park Press, pp. 92-103 (1979). Conversely, an antibody assay would be performed by bonding the complementary antigen to a surface. This procedure is unavailable in the case of an assay for hepatitis A antibody, however, as hepatitis A antigen does not adhere to the surfaces, e.g., glass and plastic, to which antigens are normally bonded.